Due to the rapid advances in science, technology, engineering, and mathematics (STEM), the United States has been at the forefront of innovation and technology development in the science, health, and biomedical fields. However, these continuing advances are in jeopardy as there is a growing national shortage of trained STEM workers. While the need for a STEM literate public and STEM workforce grows the education system has not been kept pace with STEM achievement and persistence and U.S. students consistently rank near the bottom of highly developed countries in mathematics and science. Reaching students by middle school is critical for setting them on the pathway to a STEM career. To encourage interest in STEM topics and ultimately draw more young people, particularly diverse youth, to STEM careers youth need learning opportunities that provide motivation by building on their current interests and providing real-word examples and experiences requiring context specific scientific inquiry. This project addresses these critical needs by creating Extra Innings, a serious gaming app that integrates the concepts of and complements a proven STEM curriculum, the Arizona Diamondbacks Science of Baseball, developed for use with middle school students, that is aligned with the Common Core standards, National Science Education Standards, and Next Generation Science Standards. This game-delivered STEM curriculum will leverage the widespread interest in sports to expand STEM learning opportunities for and motivate young students at a critical age when they are making decisions about their interest in STEM. The project is proposing to develop a mobile and desktop app-based serious game with a series of mini-games, each providing experiential learning around a baseball and science concept. For example, students learn about physiology and the connection between the brain, eyes, and nervous system through testing their reaction time at fielding a baseball as the ball appears on the screen. This is supplemented by an additional At the Ballpark app feature, intended to be used while at the ballpark or during a liv broadcast, that integrates live content such as statistics and pitch speed to allow the user to learn about how the science and math concepts can be used to change outcomes in a real world environment. Phase I tasks include conducting formative research to refine the game concept, including focus groups, rapid prototyping, and iterative testing, developing key concepts for content integration, completing storyboards for three game sessions, developing the architecture behind the app and programming a portion of the prototype game including three mini-game sessions, and conducting a usability evaluation to evaluate the appeal, ease of use, and utility of the game, and to measure increase in learning outcomes around the prototype content. Phase II will complete game development, conduct a rigorous evaluation, and establish the commercial model which includes purchase and sponsorship by Major League Baseball and its franchises, as was the case with the original in-person curriculum.